Ion conductive film and fuel cell using the same

ABSTRACT

Disclosed is an ion conductive film containing a composite body between an ion conductive polymer and a nitrogen-containing compound. The nitrogen-containing compound has an immobilized portion to the ion conductive polymer and exhibits an enantiomeric isomer structure when protonated. Alternatively, the nitrogen-containing compound is capable of assuming a chemical structure in which the multiple bond represented by the double bound is moved, with the atoms constituting the molecule not changing their positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2000-301383, filed Sep.29, 2000, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an ion conductive film and afuel cell using the same.

[0004] 2. Description of the Related Art

[0005] The conventional methanol fuel cell can be classified accordingto the method of supplying the liquid fuel: a liquid supply type and agasified fuel supply type. In the fuel cell of the gasified fuel supplytype, the electrode reaction is carried out between the electrode andthe gasified fuel. As a result, it is possible to obtain a highperformance with a high reactivity. On the other hand, the system ishighly complex, making it difficult to be miniaturized.

[0006] When it comes to the fuel cell of a liquid supply type, thesystem is rendered relatively simple, compared with the gasified fuelsupply type. However, since the electrode reaction is takes placebetween the electrode and the liquid fuel, the reactivity is low,leading to the problem of low performance. The liquid fuel cell utilizesthe capillary action for the supply of fuel, in a liquid state, to thefuel electrode and, thus, does not require a pump or the like.Therefore, the liquid fuel cell of this type can be miniaturized.However, the electrode reaction is weak and, thus, is low inperformance.

[0007] In addition to the problems described above, the greatest probleminherent in the fuel cell is that, where a proton conductive solidpolymer film, such as a film of perfluorosulfonic acid available underthe trade name “Nafion” from Du Pont Inc., USA, is used as anelectrolytic membrane, generated is a cross-over problem caused by thepermeation of an organic liquid fuel, such as methanol, through theelectrolytic membrane, reaches the electrode of the oxidizing agent.Where this “cross-over” phenomenon has taken place, the supplied liquidfuel reacts directly with the oxidizing agent, resulting in failure tooutput the energy as the electric power. It follows that a decisiveproblem is generated that it is impossible to obtain a stable output.

BRIEF SUMMARY OF THE INVENTION

[0008] As described above, in the conventional fuel cell, the ionconductive solid polymer film was incapable of sufficiently suppressingthe cross-over of methanol, resulting in a failure to supply a stableoutput.

[0009] The present invention, which has been achieved in view of thesituation described above, is intended to provide an ion conductive filmcapable of suppressing the cross-over of methanol, while maintaining ionconductivity.

[0010] The present invention is also intended to provide a fuel cellcapable of supplying a stable output.

[0011] According to one aspect of the present invention, there isprovided an ion conductive film having a composite body, the compositebody comprising:

[0012] an ion conductive polymer; and

[0013] a nitrogen-containing compound, having an immobilized portion tothe ion conductive polymer, and exhibiting an enantiomeric isomerstructure when protonated.

[0014] According to another aspect of the present invention, there isprovided an ion conductive film having a composite body, the compositebody comprising:

[0015] an ion conductive polymer; and

[0016] a nitrogen-containing compound capable of assuming a chemicalstructure in which the multiple bond is moved, with the atomsconstituting the molecule not changing their positions.

[0017] According to another aspect of the present invention, there isprovided a fuel cell, comprising:

[0018] an electrolytic membrane containing an ion conductive film havinga composite body between an ion conductive polymer and anitrogen-containing compound, the nitrogen-containing compound having animmobilized portion to the ion conductive polymer and exhibiting anenantiomeric isomer structure when protonated; and

[0019] a fuel electrode and an oxidizing agent electrode having theelectrolytic membrane sandwiched therebetween.

[0020] Further, according to another aspect of the present invention,there is provided a fuel cell, comprising:

[0021] an electrolytic membrane containing an ion conductive film havinga composite body between an ion conductive polymer and anitrogen-containing compound, the nitrogen-containing compound beingcapable of assuming a chemical structure in which the multiple bond ismoved, with the atoms constituting the molecule not changing theirpositions; and

[0022] a fuel electrode and an oxidizing agent electrode having theelectrolytic membrane sandwiched therebetween.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0023]FIG. 1 schematically shows as an example of the construction of amethanol fuel cell according to one embodiment of the present invention;and

[0024]FIG. 2 schematically shows the construction of a liquid fuel cellmanufactured according to the Example of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will now be described in detail.

[0026] An ion conductive film having the fluorine-containing resinrepresented by Nafion as the basic skeletal structure exhibits anexcellent ionic conductivity. The high ionic conductivity is exhibitedthrough the cluster network of a water containing state. Therefore, in afuel cell using methanol, a problem is generated in that methanolreleased from the anode is mixed with water, which passes through thecluster network. As a result, methanol is diffused into the cathode,thereby lowering the output voltage. For overcoming the problem, acrosslinked structure or the like is adopted throughout the ionconductive film so as to suppress the swelling of the ion conductivefilm. Where the entire film is crosslinked, however, a new problem isgenerated in that the conductivity is markedly lowered.

[0027] The present inventors have found, as a result of extensiveresearch, that the permeation selectivity of water and methanol can beenhanced while maintaining a high ion conductivity of the ion conductivefilm, by forming a composite material between the nitrogen-containingcompound having an enantiomeric isomer structure and the film, which isexcellent in ion conductivity but low in methanol permeability, whichlead to the present invention.

[0028] In the ion conductive film according to one embodiment of thepresent invention, it is possible for the ion conductive polymer to beprovided by, for example, a polystyrene-sulfonic acid copolymer, apolyvinyl-sulfonic acid copolymer, a crosslinked alkyl sulfonic acidderivative, a fluorine-containing polymer having a fluorine-containingresin skeleton and a sulfonic group, and a fluorine-containing polymerhaving a fluorine-containing resin skeleton and a carboxylic group.Particularly, it is most desirable for the ion conductive polymer to beprovided by a polymer having at least one of a sulfonic group and acarboxylic group and a fluorine-containing resin skeleton, in view ofdurability, film strength and ionic conductivity.

[0029] The ion conductive polymer described above can have a thicknessbetween 10 μm and 500 μm. However, it is desirable for the ionconductive polymer film to have a thickness falling within a range ofbetween 50 μm and 200 μm in view of the balance of mechanical strengthand electric conductivity.

[0030] The ion conductive film according to one embodiment of thepresent invention is formed of a composite body comprising the ionconductive polymer described above and a specified nitrogen-containingcompound having a molecular weight not higher than 1000.

[0031] The nitrogen-containing compound used in the present invention isrequired to have an immobilized portion to the ion conductive polymerand an enantiomeric isomer structure when protonated. Incidentally, thenitrogen-containing compound having an enantiomeric isomer structurewhen protonated represents a nitrogen compound capable of assuming achemical structure in which the multiple bonds represented by a doublebond is moved, with the atoms constituting the molecule not changingtheir positions. To be more specific, the particular nitrogen-containingcompound used in the present invention includes, for example, imidazole,guanidine, triazole and derivatives thereof.

[0032] Incidentally, two systems are known to the art as the protonmoving type relating to the proton conductivity. In general, protons aretransferred under a hydrated state together with the migration of water.If the proton conductance within the electrolytic membrane of a fuelcell is generated in such a mechanism, methanol is also transferredtogether with water, resulting in the cross-over of methanol. TheGrottus mechanism is known to the art as the proton conductivitymechanism in which water is not involved. The Grottus mechanismrepresents the proton moving method in which the proton is seeminglymoved while jumping over the methanol molecules. In the Grottusmechanism, water is not involved in the proton migration, making ispossible to realize the selective migration of the proton. It is knownto the art that the Grottus mechanism can be realized by using a part ofthe hydrogen bondable enantiomeric isomer. However, it was previouslyimpossible to ensure a proton conductivity sufficient for practicallevel, using the Grottus mechanism.

[0033] The present inventors have found that, where a composite body isformed by a nitrogen-containing compound having a portion bonded to theion conductive polymer and also having a nitrogen-containingenantiotopic isomer structure and an ion conductive film, it is possibleto ensure a practical proton conductivity and to lower the methanolpermeability. It is possible for the coupling portion of thenitrogen-containing compound with the ion conductive polymer to be anyof a hydrogen bond, a ionic bond and a covalent bond. Particularly, thenitrogen-containing compound used in the present invention includes, forexample, imidazole, triazole, guanidine and derivatives thereof. To bemore specific, the nitrogen-containing compound used in the presentinvention includes, for example, guanidino benzimidazole, guanine,guanidine carbonate, purine, diamino purine, diamino triazole,histamine, and salts thereof. Particularly, guanidine carbonate exhibitsexcellent characteristics when a composite body is formed together witha fluorine-containing sulfonic acid.

[0034] Incidentally, the “composite body” referred to in the presentspecification represents the state in which the ion conductive polymerand a specified nitrogen-containing compound are bonded to each other byan ionic bond. To be more specific, a composite body according to oneembodiment of the present invention can be formed by the mutual functionwith a carboxylic acid or with a carbocation serving to achieve thecoupling between a carboxylic acid and nitrogen. It is desirable for themolecular weight of the nitrogen-containing compound to be not higherthan 1000 because, if the molecular weight of the nitrogen-containingcompound exceeds 1000, it is difficult for the nitrogen-containingcompound to form a composite body together with the ion conductivepolymer.

[0035] Where a fluorine-containing sulfonic acid constitutes the ionconductive polymer in the composite body described above, it isdesirable for the nitrogen-containing compound to be contained in anamount of about 1 to 50,000 ppm of the fluorine-containing sulfonicacid. Where the amount of the nitrogen-containing compound is smallerthan 1 ppm, it is difficult to obtain the effect of suppressing themethanol permeation. On the other hand, where the amount of thenitrogen-containing compound exceeds 50,000 ppm, the proton conductivitytends to be lowered. It is more desirable for the amount of thenitrogen-containing compound to fall within a range of between 10 ppmand 10,000 ppm of the fluorine-containing sulfonic acid.

[0036] In the ion conductive film according to one embodiment of thepresent invention, the nitrogen-containing compound produces its effectin each of the cases where the nitrogen-containing compound is coated onthe surface and impregnated in the ion conductive film. Where thenitrogen-containing compound is coated on the surface of the ionconductive film, it is desirable for the ion conductive film to be thinbecause the decrease in the electric conductivity of the film islowered. The ion conductive film, which is generally 0.01 to 10 μmthick, should desirably be 0.1 to 1 μm thick. Also, it is possible forthe nitrogen-containing compound to be coated on one surface of the ionconductive film or to be sandwiched between two ion conductive films.

[0037] A film containing a nitrogen-containing compound can be obtainedby, for example, preparing a solution by dissolving anitrogen-containing compound and another soluble ion conductivesubstance in a suitable solvent, followed by coating a film of an ionconductive polymer with the resultant solution. The solvent used forpreparing the solution includes, for example, water, alcohol, ether andester. Also, the “another ion conductive substance” noted aboveincludes, for example, a carbonate, a hydrochloride and a sulfate.

[0038] It is also possible to prepare an ion conductive film accordingto one embodiment of the present invention by a laminating method or animmersion method in addition to the coating method. In this case, it ispossible to apply a pressing or heat treatment. Where the ion conductivefilm is prepared by the immersion method, it is desirable for theconcentration of the nitrogen-containing compound in the solution usedto be low. To be more specific, a better effect can be obtained by thetreatment with a low concentration not higher than 0.1%.

[0039] It is possible to increase the electric conductivity of the filmby doping the ion conductive film in the form of the composite bodydescribed above with an organic acid or an inorganic acid such asperfluoromethane sulfonic acid, perfluoro acetic acid, phosphoric acidor nitric acid. The concentration of the doped organic acid or inorganicacid can be determined appropriately depending on the ratio of theconductivity to the methanol permeability used.

[0040] It is possible to promote the crosslinkage of the ion conductivefilm according to one embodiment of the present invention, whichcontains a composite body between an ion conductive polymer and anitrogen-containing compound, by irradiation with an energy beam such asan electron beam (EB), gamma rays, ultraviolet light or by the heatingwith a microwave or with a heater so as to suppress the swelling of theion conductive film. In general, an EB reaches a deep portion of thefilm and, thus, where the ion conductive film is irradiated with an EB,it is desirable to set the accelerating voltage at 100 kV or less. Wherethe accelerating voltage exceeds 100 kV, the damage done to the film isexcessively large or the EB reaches a deep portion of the film, with theresult that it is difficult to obtain a desired film. In order to obtaina sufficient effect, it is desirable for the accelerating voltage to be20 kV or more. The particular treatment can be performed either withinan inert gas atmosphere or within air, though reproducible effect can beobtained when EB irradiation is carried out under an inert gasatmosphere.

[0041] The methanol fuel cell according to one embodiment of the presentinvention will now be described with reference to the accompanyingdrawings.

[0042]FIG. 1 schematically shows the construction of a fuel cellaccording to one embodiment of the present invention. Incidentally, FIG.1 simply shows a stacked body 100 and a liquid fuel introduction path 4.It should be noted in this connection that a liquid fuel is introducedfrom a fuel tank (not shown) into the liquid fuel introduction path 4via an introducing pipe (not shown).

[0043] As shown in FIG. 1, the stacked body 100 is prepared by stackinga plurality of unit cells one upon the other. In each unit cell, anelectrolyte plate 1 is held between a fuel electrode (anode) 2 and anoxidizing agent electrode (cathode) 3. An electromotive section 10 isformed by the electrolyte plate 1, the fuel electrode 2 and theoxidizing agent electrode 3. Each of the fuel electrode 2 and theoxidizing agent electrode 3 is formed of a conductive porous body suchthat the fuel and the oxidizing agent gas as well as electrons can becirculated therethrough.

[0044] Further, each unit cell includes a fuel permeating section 6capable of performing the function of holding the liquid fuel and a fuelevaporating section 7 for guiding the evaporated fuel evaporated fromthe liquid fuel held by the fuel permeating section 6 to the fuelelectrode 2. The fuel evaporating section 7 is arranged between the fuelpermeating section 6 and the fuel electrode 2. A plurality of unit cellseach including the fuel permeating section 6, the fuel evaporatingsection 7 and the electromotive section 10 are stacked one upon theother with a separator 5 interposed therebetween so as to form thestacked type fuel cell 100. It should be noted that an oxidizing agentgas supply groove 8 is formed as a continuous groove on that surface ofthe separator 5 which faces the oxidizing agent electrode 3.

[0045] Incidentally, as a means for supplying a liquid fuel from thefuel tank into the fuel permeating section 6 of the unit cell, it isconceivable to form the liquid fuel introduction path 4 joined to thefuel tank on at least one side surface of the stacked fuel cell 100. Theliquid fuel introduced into the liquid fuel introduction path 4 issupplied through the side surface of the stacked fuel cell 100 to thefuel permeating section 6 and, then, evaporated in the fuel evaporatingsection 7. Further, the evaporated fuel is supplied to the fuelelectrode 2. It should be noted that, where the fuel permeating section6 is formed of a material producing a capillary action, it is possibleto supply the liquid fuel to the fuel permeating section 6 by capillaryaction without using auxiliary equipment. For capillary action to beeffective, it is necessary for the fuel cell to be constructed such thatthe liquid fuel introduced into the liquid fuel introduction path 4 isin direct contact with one end of the fuel permeating section 6. It isalso necessary for the region between the liquid fuel introduction path4 and the stacked fuel cell 100 to be insulated, except for the regionto which the fuel permeating section 6 is connected, though theinsulation is omitted in FIG. 1.

[0046] Where the stacked fuel cell 100 is prepared by stacking aplurality of unit cells one upon the other as shown in FIG. 1, theseparator 5, the fuel permeating section 6 and the fuel evaporatingsection 7 also perform the function of a collecting plate for conductingthe generated electrons and, thus, are formed of a conductive materialsuch as a porous body containing carbon. Further, a stratum-like, anisland-like or granular catalyst layer is formed as required between thefuel electrode 2 and the electrolyte plate 1 and between the oxidizingagent electrode 3 and the electrolyte plate 1.

[0047] It is also possible for the fuel electrode 2 itself and theoxidizing agent electrode 3 itself to perform the function of a catalystelectrode. It is possible for the catalyst electrode to be of asingle-layered structure comprising a catalyst layer alone or of amulti-layered structure comprising a substrate such as a conductivepaper or cloth and a catalyst layer formed on the substrate.

[0048] As described above, the separator 5 included in the unit cellshown in FIG. 1 also performs the function of a channel allowing theflow of the oxidizing agent gas. By using the separator 5 performing thefunctions of both the separator and the channel, i.e., achanneling-separator 5, the number of parts used can be decreased so asto further miniaturize the fuel cell. It is also possible to use anordinary channel in place of the particular separator 5.

[0049] For supplying a liquid fuel from the fuel storing tank (notshown) into the liquid fuel introduction path 4, the liquid fuel housedin the fuel storing tank is subjected to, for example, free fall so asto be introduced into the liquid fuel introduction path 4. This methodpermits introducing the liquid fuel into the liquid fuel introductionpath 4 without fail, though there is a structural limitation in that thefuel storing tank must be positioned higher than the upper surface ofthe stacked fuel cell 100. It is also possible that the liquid fuel issucked from the fuel storing tank by the capillary action of the liquidfuel introduction path 4. In the case of employing this method, it isunnecessary to make the connection between the fuel storing tank and theliquid fuel introduction path 4, i.e., the position of the fuel inletport formed in the liquid fuel introduction path 4, higher than theupper surface of the stacked fuel cell 100. It follows that, if thismethod is combined with, for example, the free fall method, it ispossible to obtain a merit that the installing position of the fuel tankcan be set freely.

[0050] It should be noted, however, that, in order to smoothly supplythe liquid fuel, which is introduced into the liquid fuel introductionpath 4 by capillary action, into the fuel permeating portion 6 bycapillary action, it is desirable for the force of the capillary actionproduced by the fuel permeating section 6 to be set greater than theforce of the capillary action produced in the liquid fuel introductionpath 4. Incidentally, in the embodiment shown in the drawing, only oneliquid fuel introduction path 4 is arranged along the side surface ofthe stacked fuel cell 100. However, it is also possible to form anotherliquid fuel introduction path 4 along the other side surface of thestacked fuel cell 100.

[0051] The fuel storing tank described above can be made detachable fromthe stacked fuel cell 100. As a result, the cell can be operated for along time by replacing the fuel storing tank. Also, the liquid fuel canbe supplied from the fuel storing tank into the liquid fuel introductionpath 4 by utilizing free fall as described above, by pressing the tankso as to expel the liquid fuel, or by drawing the fuel out by capillaryaction via the liquid fuel introduction path 4.

[0052] As described above, the liquid fuel introduced into the liquidfuel introduction path 4 is supplied into the fuel permeating section 6.The type of fuel permeating section 6 is not particularly limited aslong as it is capable of holding the liquid fuel inside the fuelpermeating section 6 and is capable of supplying the evaporated fuelalone into the fuel electrode 2 though the fuel evaporating section 7.For example, it is possible for the fuel permeating section 6 to includea gas-liquid separating membrane, which acts as a liquid fuelpassageway, at the interface with the fuel evaporating section 7.Further, where a liquid fuel is supplied to the fuel permeating section6 by the force of the capillary action, the type of fuel permeatingsection 6 is not particularly limited as long as the liquid fuel iscapable of passing through the fuel permeating section 6 by capillaryaction. For example, it is possible for the fuel permeating section 6 tobe formed of a porous body comprising particles or a filler, a unwovenfabric prepared by the paper-making method, a woven fabric prepared byweaving fibers, and small clearances formed between the fuel permeatingsection 6 and a plate made of glass or a plastic material.

[0053] In the case where a porous body is used for forming the fuelpermeating section 6, the capillary action of the porous body itselfforming the fuel permeating section 6 can be utilized as the force ofthe capillary action for sucking the liquid fuel into the fuelpermeating section 6. In the case of utilizing the capillary action,prepared is an open cell structure in which pores of the fuel permeatingsection 6 made of a porous body are continuous and the pore diameter iscontrolled. It should be noted that the open cell is allowed to extendfrom the side surface of the fuel permeating section 6 of the liquidfuel introduction path 4 to reach at least the other surface, with theresult that the liquid fuel can be smoothly supplied in the lateraldirection by the capillary action.

[0054] The pore diameter of the porous body used for forming the fuelpermeating section 6 is not particularly limited, as far as the fuelpermeating section 6 is capable of sucking the liquid fuel from withinthe liquid fuel introduction path 4. However, it is desirable for thepore diameter to fall within a range of between about 0.01 μm and 150 μmin view of the force of the capillary action of the liquid fuelintroduction path 4. It is also desirable for the area ratio of thepores, which provides the index of the pore continuity within the porousbody, to fall within a range of between about 20% and 90%. If the porediameter is smaller than 0.01 μm, it is difficult to manufacture thefuel permeating section 6. On the other hand, if the pore diameterexceeds 150 μm, the capillary action tends to be weakened. Also, if thearea ratio of the pore is less than 20%, the amount of the open cell isdecreased, with the amount of the closed cell increased, resulting in afailure to obtain a sufficient capillary action. On the other hand, ifthe area ratio of the pore exceeds 90%, the amount of the open cell iscertainly increased. However, the mechanical strength of the fuelpermeating section 6 is lowered so as to make it difficult tomanufacture the fuel permeating section 6. In practice, it is desirablefor the pore diameter to fall within a range of between 0.5 μm and 100μm and for the pore area ratio to fall within a range of between 30% and75%.

[0055] The present invention will now be described in more in detailwith reference to Examples. Needless to say, the technical scope of thepresent invention is not limited by the Examples which follow.

[0056] Ion conductive films for Examples 1 to 5 were prepared bycombining ion exchange resin films (Nafion films) and process solutionscontaining predetermined concentrations of nitrogen-containingcompounds, as shown in Table 1 below.

[0057] In preparing the ion conductive film, each of the ion conductiveresin films was dipped in the process solution for one hour at 100° C.,followed by washing at room temperature and subsequently pressing thewashed ion exchange resin film.

[0058] Then, the unit cell constructed as shown in FIG. 2 was preparedas follows by using the resultant ion conductive film as the electrolytefilm 1. In the first step, prepared were the fuel electrode 2 sized at32 mm×32 mm and formed of a Pt—Ru series catalyst layer formed on acarbon cloth and the oxidizing agent electrode 3 sized at 32 mm×32 mmand formed of a Pt black catalyst layer formed on a carbon cloth. Theion conductive film forming the electrolyte membrane 1 was held betweenthe fuel electrode 2 and the oxidizing agent electrode 3 such that thecatalyst layers were in direct contact with the ion conductive film, toobtain a laminate structure. The laminate structure thus obtained wassubjected to a hot pressing at 120° C. for 5 minutes under a pressure of100 kg/cm² so as to obtain the electromotive section 10.

[0059] Further, the unit cell constructed as shown in FIG. 2 wasprepared by incorporating the electromotive section 10 thus obtained inthe system including the fuel evaporating section 7 comprising a porouscarbon plate having an average pore diameter of 100 μm and a porosity of70%, the fuel permeating section 6 comprising a carbon porous platehaving an average pore diameter of 5 μm and a porosity of 40%, anoxidizing agent electrode holder 11, and a fuel electrode holder 9. Thereaction area of the unit cell thus prepared was 10 cm². Incidentally,the oxidizing agent electrode holder 11 was provided with an oxidizingagent gas supply groove 8 having a depth of 2 mm and a width of 1 mm.

[0060] As shown in FIG. 2, a liquid fuel 20 is introduced into the fuelpermeating section 6 and, after the electrode reaction, a CO₂ gas 21 isreleased from the fuel evaporating section 7.

[0061] A mixture of methanol and water mixed at 1:1 molar ratio wasintroduced as the liquid fuel 20 into the liquid fuel cell thus obtainedby utilizing the capillary action from the side surface of the fuelpermeating section 6. At the same time, the air of 1 atm. used as theoxidizing agent gas was allowed to flow through the gas channel 8 at therate of 100 ml/min so as to achieve electric power generation.

[0062] Further, an additional unit cell was also prepared as above,except that an unprocessed Nafion film was used as the electrolytemembrane, so as to provide a Comparative Example.

[0063] Table 1 shows the conductivity and the relative methanolpermeability of each ion conductive film and the fuel cellcharacteristics together with the ion exchange resin film and theprocess solution used. The methanol permeability is indicated as arelative value with the methanol conductivity of the unprocessed Nafionfilm (Comparative Example 1) set at 1. TABLE 1 Maximum power generationin the Ion Methanol case of using 20% exchange Nitrogen- permeationResistance aqueous methanol resin containing compound amount of cellsolution Relative (mΩ) (mW/cm²) value with Nafion 117 set at 1 Example 1Nafion 117 Guanidium carbonate 0.5 30 20 (0.01% aqueous solution)Example 2 Nafion 1135 Guanidium carbonate 0.3 30 25 (0.03% aqueoussolution) Example 3 Nafion 115 Guanidium carbonate 0.3 35 20 (0.02%aqueous solution) Example 4 Nafion 117 Guanidino 0.5 40 17 benzimidazole(treated with 0.01% aqueous solution) Example 5 Nafion 11 7 Diaminopurine (0.01% 0.5 40 16 aqueous solution) Comparative Nafion 117 None 130 2 Example 1

[0064] As is apparent from Table 1, the ion conductive films of Examples1 to 5, which was substantially equal in electrical conductivity to theunprocessed Nafion film (Comparative Example 1), was found to exhibitthe methanol permeability markedly lower than that for ComparativeExample 1.

[0065] In the fuel cell prepared by using the unprocessed Nafion film117 as the electrolyte membrane, the cross-over was excessively large inthe case of using a 20% methanol solution, as is apparent fromComparative Example 1, with the result that the maximum power generationwas only 2 mW/cm². On the other hand, when it comes to the unit cellusing the ion conductive film containing the composite body of Examples1 to 5 of the present invention, the cross-over was suppressed, leadingto satisfactory power generation. This indicates that the composite filmin the Examples of the present invention permits a more effectivelowering of the methanol permeability while maintaining the electricalconductivity inherent in the Nafion film.

[0066] As described above in detail, the present invention provides anion conductive film, which permits suppressing the cross-over ofmethanol while maintaining the ion conductivity.

[0067] The present invention also provides a fuel cell capable ofproducing a stable output.

[0068] The present invention makes it possible to provide a fuel cellsmall in size, high in performance, and capable of supplying a stableoutput and, thus, has a markedly high industrial value.

[0069] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the present invention in itsbroader aspects is not limited to the specific details andrepresentative embodiments shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. An ion conductive film having a composite body,said composite body comprising: an ion conductive polymer; and anitrogen-containing compound, having an immobilized portion to said ionconductive polymer, and exhibiting an enantiomeric isomer structure whenprotonated.
 2. The ion conductive film according to claim 1, whereinsaid ion conductive polymer is a polymer containing at least one of asulfonic group and a carboxyl group and a fluorine-containing resinskeleton.
 3. The ion conductive film according to claim 1, wherein saidnitrogen-containing compound is at least one compound selected from thegroup consisting of guanidine, triazole and derivatives thereof.
 4. Theion conductive film according to claim 1, wherein the molecular weightof said nitrogen-containing compound is not higher than
 1000. 5. The ionconductive film according to claim 1, wherein said ion conductivepolymer is a fluorine-containing sulfonic acid and the amount of saidnitrogen-containing compound falls within a range of between 1 ppm and50,000 ppm based on said fluorine-containing sulfonic acid.
 6. An ionconductive film having a composite body, said composite body comprising:an ion conductive polymer; and a nitrogen-containing compound capable ofassuming a chemical structure in which the multiple bond is moved, withthe atoms constituting the molecule not changing their positions.
 7. Theion conductive film according to claim 6, wherein said ion conductivepolymer is a polymer containing at least one of a sulfonic group and acarboxyl group and a fluorine-containing resin skeleton.
 8. The ionconductive film according to claim 6, wherein said nitrogen-containingcompound is at least one compound selected from the group consisting ofguanidine, triazole and derivatives thereof.
 9. The ion conductive filmaccording to claim 6, wherein the molecular weight of saidnitrogen-containing compound is not higher than
 1000. 10. The ionconductive film according to claim 6, wherein said ion conductivepolymer is a fluorine-containing sulfonic acid and the amount of saidnitrogen-containing compound falls within a range of between 1 ppm and50,000 ppm based on said fluorine-containing sulfonic acid.
 11. A fuelcell, comprising: an electrolytic membrane containing an ion conductivefilm having a composite body between an ion conductive polymer and anitrogen-containing compound, said nitrogen-containing compound havingan immobilized portion to said ion conductive polymer and exhibiting anenantiomeric isomer structure when protonated; and a fuel electrode andan oxidizing agent electrode having said electrolytic membranesandwiched therebetween.
 12. The fuel cell according to claim 11,wherein said ion conductive polymer is a polymer containing at least oneof a sulfonic group and a carboxyl group and a fluorine-containing resinskeleton.
 13. The fuel cell according to claim 11, wherein saidnitrogen-containing compound is at least one compound selected from thegroup consisting of guanidine, triazole and derivatives thereof.
 14. Thefuel cell according to claim 11, wherein the molecular weight of saidnitrogen-containing compound is not higher than
 1000. 15. The fuel cellaccording to claim 11, wherein said ion conductive polymer is afluorine-containing sulfonic acid and the amount of saidnitrogen-containing compound falls within a range of between 1 ppm and50,000 ppm based on said fluorine-containing sulfonic acid.
 16. A fuelcell, comprising: an electrolytic membrane containing an ion conductivefilm having a composite body between an ion conductive polymer and anitrogen-containing compound, said nitrogen-containing compound beingcapable of assuming a chemical structure in which the multiple bond ismoved, with the atoms constituting the molecule not changing theirpositions; and a fuel electrode and an oxidizing agent electrode havingsaid electrolytic membrane sandwiched therebetween.
 17. The fuel cellaccording to claim 16, wherein said ion conductive polymer is a polymercontaining at least one of a sulfonic group and a carboxyl group and afluorine-containing resin skeleton.
 18. The fuel cell according to claim16, wherein said nitrogen-containing compound is at least one compoundselected from the group consisting of guanidine, triazole andderivatives thereof.
 19. The fuel cell according to claim 16, whereinthe molecular weight of said nitrogen-containing compound is not higherthan
 1000. 20. The fuel cell according to claim 16, wherein said ionconductive polymer is a fluorine-containing sulfonic acid and the amountof said nitrogen-containing compound falls within a range of between 1ppm and 50,000 ppm based on said fluorine-containing sulfonic acid.